Profiled sputtering target and method of making the same

ABSTRACT

A sputtering target comprising a sputtering material and having a non-planar sputtering surface prior to erosion by use in a sputtering system, the non-planar sputtering surface having a circular shape and comprising a central axis region including a concave curvature feature at the central axis region. The central axis region having a wear profile after erosion by use in a sputtering system for at least 1000 kWhrs including a protuberance including a first outer circumferential wear surface having a first slope. A reference, protruding convex curvature feature for a reference target after sputtering use for the same time includes a second outer circumferential wear surface having a second slope. The protuberance provides a sputtered target having reduced shadowing relative to the reference, protruding convex curvature feature, wherein the first slope is less steep than a second slope.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Provisional Application No.62/487,617, filed Apr. 20, 2017, which is herein incorporated byreference in its entirety.

FIELD OF THE INVENTION

The field of the subject matter is the design and use of sputteringsystems including targets having a central axis region geometry toprovide longer target life and uniform film deposition.

DESCRIPTION OF RELATED ART

Electronic and semiconductor components are used in ever-increasingnumbers of consumer and commercial electronic products, communicationsproducts and data-exchange products. Examples of some of these consumerand commercial products are televisions, computers, cell phones, pagers,handheld organizers, portable music players and radios, car stereos, andremote controls. As the demand for these consumer and commercialelectronics increases, there is also a demand for those same products tobecome smaller and more portable for the consumers and businesses.

As a result of the size decrease in these products, the components thatcomprise the products must also become smaller and/or thinner. Examplesof some of those components that need to be reduced in size or scaleddown are microelectronic chip interconnections, semiconductor chipcomponents, resistors, capacitors, printed circuit or wiring boards,wiring, keyboards, touch pads, and chip packaging.

When electronic and semiconductor components are reduced in size orscaled down, any defects that are present in the larger components aregoing to be exaggerated in the scaled down components. Thus, the defectsthat are present or could be present in the larger component should beidentified and corrected, if possible, before the component is scaleddown for the smaller electronic products.

In order to identify and correct defects in electronic, semiconductorand communications components, the components, the materials used andthe manufacturing processes for making those components should be brokendown and analyzed. Electronic, semiconductor andcommunication/data-exchange components are composed, in some cases, oflayers of materials, such as metals, metal alloys, ceramics, inorganicmaterials, polymers, or organometallic materials. The layers ofmaterials are often thin (on the order of less than a few tens ofangstroms in thickness). In order to improve on the quality of thelayers of materials, the process of forming the layer—such as physicalvapor deposition of a metal or other compound—should be evaluated and,if possible, modified and improved.

In order to improve the process of depositing a layer of material, thesurface and/or material composition must be measured, quantified anddefects or imperfections detected. In the case of the deposition of alayer or layers of material, it is not the actual layer or layers ofmaterial that should be monitored but the material and surface of thatmaterial that is being used to produce the layer of material on asubstrate or other surface. For example, when depositing a layer ofmetal onto a surface or substrate by sputtering a target comprising thatmetal, the atoms and molecules being deflected or liberated from thetarget must travel a path to the substrate or other surface that willallow for an even and uniform deposition. Atoms and molecules travelingnatural and expected paths after deflection and/or liberation from thetarget can unevenly deposit on the surface or substrate, includingtrenches and holes in the surface or substrate. For certain surfaces andsubstrates, it may be necessary to redirect the atoms and moleculesleaving the target in order to achieve a more uniform deposition,coating and/or film on the surface or substrate.

In DC magnetron sputtering systems, the buildup of insulating layer onpoorly eroding race tracks and subsequent arcing on such layer have beenthe important issues for both process engineers and targetmanufacturers. Well-eroding and poorly-eroding “race tracks” develop dueto the nature of magnet configuration. On the poorly eroding racetracks, insulating layers build up slowly with target usage (i.e., oxideor nitride films for Al, Ta, and Ti targets). Eventually, the chargeaccumulation on the dielectric layer leads to arcing and particlegeneration. The propensity of arcing increases with target usage becauseof the buildup of dielectric layer.

A schematic view of a portion of an exemplary physical vapor depositionapparatus 10 is illustrated in FIG. 1. A sputtering assembly 10comprises a backing plate 12 having a sputtering target 14 bondedthereto. Sputtering target 14 has a planar sputter surface 16. Asemiconductive material wafer 18 is within the assembly 10 and providedto be spaced from sputtering surface 16 of target 14. In operation,particles or sputtered material 22 is displaced from surface 16 oftarget 14 and used to form a coating (or thin film) 20 on wafer 18.

Typically the target forms part of a cathode assembly in a PVD chamberthat contain a process gas such as argon. The electrical field isapplied between the cathode assembly and an anode in the chamber(typically the sidewall of PVD apparatus) and, as a result, the gas isionized by collision with electrons ejected from the surface of thecathode. This generates a plasma of positively charged gas ions that areaccelerated towards the negatively charged target surface. The positivegas ions impact the target and dislodge particles from the targetmaterial. Once freed from the target, these displaced (and essentiallyneutral) particles travel across the plasma and deposit themselves uponthe wafer substrate as a thin film.

There are several important parameters that govern effectiveness ofsputtering. Those include uniformity and reflectivity of deposited thinfilm, the number of defects (foreign particles) on substrate, depositionrate, current-voltage (I-V) characteristics during deposition and targetlife.

Deposition by sputtering can be non-uniform for various reasons. Plasmadensity can be affected by the geometry of PVD equipment. The magneticfield can change non-uniformly due to variation among the magnets, whichare in motion, or in the relationship of the magnets to the target.Finding the optimal arrangement and rotational speed of magnets locatedbehind target backside in order to influence the path taken by electronswithin the sputtering chamber, to increase the rate of collisions of gasand achieve better sputtering rate and uniformity of deposited thinfilms, can be challenging. In some cases, temperature variation atdifferent locations on the target as well as grain size and texture ofthe target material may also result in non-uniform deposition.

In general, atoms are ejected from target surface with a widedistribution of angles. However collisions with other particles and gasscattering randomize the trajectories of atoms due to small mean path ofejected metal atoms relative to the total travelled distance betweentarget and wafer. Low pressure (high vacuum) has been thereforeimplemented to limit the number of collisions and reduce randomization.

Another source of non-uniform deposition comes from the changing shapeof the target surface as the target gets eroded away during sputtering.This erosion profile can also be affected by magnet arrangement andmovement. Conventional target designs at the beginning of life generallyinclude a planar surface geometry at the center of the sputtering targetas shown in FIG. 1. A need exists for extending target life to improvethin film uniformity.

SUMMARY OF THE INVENTION

These and other needs are addressed by the various aspects, embodiments,and configurations of the present disclosure.

Embodiments of the present disclosure include a sputtering targetcomprising a sputtering material and having a non-planar sputteringsurface prior to erosion by use in a sputtering system, the non-planarsputtering surface having a circular shape and comprising: a centralaxis region having a center axis; a concave curvature feature at thecentral axis region, the concave curvature feature symmetricallydisposed about the center axis and having a first point coincident withthe center axis, the concave curvature feature corresponding to areference, protruding convex curvature feature of an erosion profile ofa reference sputtering target following erosion by use in a sputteringsystem for at least 1000 kWhrs and coincident with the center axis, thereference sputtering target comprising a sputtering material having anidentical composition as the sputtering material of the sputteringtarget, the reference sputtering target further comprising a planarsputtering surface prior to erosion by use in a sputtering system; thecentral axis region having a wear profile after erosion by use in asputtering system for at least 1000 kWhrs including a protuberanceincluding a first height and a first outer circumferential wear surfacehaving a first slope and the reference, protruding convex curvaturefeature including a second height and a second outer circumferentialwear surface having a second slope, the protuberance providing asputtered target having reduced shadowing relative to the reference,protruding convex curvature feature, wherein: the first height is lessthan the second height, the reference, protruding convex curvaturefeature having the second height blocking more sputtered atoms havingtrajectories directed radially inward toward the central axis andredepositing onto the target; and, the first slope is less steep thanthe second slope, the second outer circumferential wear surface havingthe second slope directing more sputtered atoms with trajectoriesradially outward relative the central axis away from a wafer.

The sputtering target according to paragraph [0016], wherein thepercentage reduction between the first slope and the second slope is atleast about 40 percent.

The sputtering target according to either paragraph [0016] or paragraph[0017], wherein the percentage reduction between the first slope and thesecond slope is from about 40 percent to about 100 percent.

The sputtering target according to any of paragraphs [0016]-[0018], thecentral axis region further including a total target thickness at thecenter axis, wherein the total target thickness is from about 10 percentto about 30 percent less than the total target thickness at the centeraxis for the reference sputtering target comprising the planarsputtering surface prior to erosion.

The sputtering target according to any of paragraphs [0016]-[0019],wherein the total target thickness is from about 15 percent to about 25percent less than the total target thickness at the center axis for thereference sputtering target.

The sputtering target according to any of paragraphs [0016]-[0020],wherein the sputtering target further comprises at least one recessedgroove in the surrounding region.

The sputtering target according to any of paragraphs [0016]-[0021],wherein the sputtering material includes at least one material chosenfrom Ti, Al, Cu, Ta, Ni, Co, Mo, Au, Ag, Pt, W, Cr, a Ti alloy, an Alalloy, a Cu alloy, a Ta alloy, a Ni alloy, a Co alloy, a Mo alloy, a Aualloy, a Ag alloy, a Pt alloy, a W alloy, and a Cr alloy.

The sputtering target according to any of paragraphs [0016]-[0022],wherein the target is monolithic.

The sputtering target according to any of paragraphs [0016]-[0023],wherein the target is diffusion bonded.

Embodiments of the present disclosure also include a method of designinga sputtering target for use in a sputtering chamber, said methodcomprising: forming a sputtering target having a surface profile havinga concave curvature feature symmetrically about a central axis of thesputtering target; measuring a sputtered profile of the sputteringtarget after sputtering in a sputtering chamber for at least 1000 kWhrs;designing a revised surface profile based on the measurements of thesputtered profile to reduce shadowing at a central axis region of thesputtering target; and forming a revised sputtering target having therevised surface profile.

The method according to paragraph [0025], further including measuring asputtered profile of a reference sputtering target after use for atleast 1000 kWhrs, the reference sputtering target comprising asputtering material having an identical composition as the sputteringmaterial of the sputtering target, the reference sputtering targetfurther comprising a planar sputtering surface prior to erosion by usein a sputtering system, wherein: the measured sputtered profile of thesputtering target includes a first outer circumferential wear surfacehaving a first slope; and, the measured reference sputtering targetincludes a second outer circumferential wear surface having a secondslope wherein the first slope is less steep than the second slope.

The method according to either paragraph [0025] or paragraph [0026],wherein the percentage reduction between the first slope and the secondslope is at least about 40 percent.

The method according to any of paragraphs [0025]-[0027], wherein thesteps of measuring, designing, and forming a revised sputtering targetare repeated to optimize the revised surface profile.

Embodiments of the present disclosure include a sputtering targetcomprising a sputtering material having a non-planar sputtering surfaceprior to erosion by use in a sputtering system, the non-planarsputtering surface having a circular shape and comprising: a centralaxis region having a center axis; the central axis region including atleast one non-protruding concave curvature feature symmetricallydisposed about the center axis and having a first point coincident withthe center axis, the at least one non-protruding concave curvaturefeature corresponding to a reference, protruding convex curvaturefeature of an erosion profile of a reference sputtering target followingerosion by use in a sputtering system and coincident with the centeraxis, the reference sputtering target comprising a sputtering materialhaving an identical composition as the sputtering material of thesputtering target, the reference sputtering target further comprising aplanar sputtering surface prior to erosion by use in a sputteringsystem; a line perpendicular to the center axis and colinear with thereference sputtering target planar sputtering surface prior to erosionby use in a sputtering system; the first point at a first axial distancefrom the line; a surrounding region disposed about the central axisregion; the surrounding region including a second point coincident withthe line and at a first radial distance from the center axis; thecentral axis region having a wear profile after erosion by use in asputtering system including a protuberance having a third pointcoincident with the center axis and at a second axial distance from theline and a fourth point at the first radial distance from the centeraxis and at a third axial distance from the line, wherein the thirdaxial distance is greater than or equal to the first axial distance andto the second axial distance.

The sputtering target according to paragraph [0029], wherein thereference sputtering target has a wear profile after use including afifth point coincident with the center axis at a fourth axial distancefrom the line, wherein the first axial distance and the second axialdistance are greater than the fourth axial distance.

The sputtering target according to either paragraph [0029] or paragraph[0030], wherein the protuberance includes a first outer circumferentialwear surface having a first slope and the reference, protruding convexcurvature feature includes a second outer circumferential wear surfacehaving a second slope, wherein the first slope is less steep than thesecond slope.

The sputtering target according to any of paragraphs [0029]-[0031],wherein the at least one non-protruding concave curvature featureincludes an inner circumferential surface and a bottom surface includingthe first point.

The sputtering target according to any of paragraphs [0029]-[0032],wherein the bottom surface is flat, rounded, concave, or convex.

The sputtering target according to any of paragraphs [0029]-[0033],wherein the sputtering target has a total target radius and a totaltarget thickness, wherein the first radial distance is from about 5percent to about 40 percent relative to the total target radius and thefirst axial distance is from about 5 percent to about 50 percent of thetotal target thickness.

The sputtering target according to any of paragraphs [0029]-[0034],wherein the sputtering material includes at least one material chosenfrom Ti, Al, Cu, Ta, Ni, Co, Mo, Au, Ag, Pt, W, Cr, a Ti alloy, an Alalloy, a Cu alloy, a Ta alloy, a Ni alloy, a Co alloy, a Mo alloy, a Aualloy, a Ag alloy, a Pt alloy, a W alloy, and a Cr alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated into and form a part of thespecification to illustrate several examples of the present disclosure.These drawings, together with the description, explain the principles ofthe disclosure. The drawings simply illustrate preferred and alternativeexamples of how the disclosure can be made and used and are not to beconstrued as limiting the disclosure to only the illustrated anddescribed examples. Further features and advantages will become apparentfrom the following, more detailed, description of the various aspects,embodiments, and configurations of the disclosure, as illustrated by thedrawings referenced below.

FIG. 1 is a schematic view illustrating of a portion of an exemplaryphysical vapor deposition apparatus 10.

FIG. 2 is a schematic view illustrating systems using a collimator as inthe prior art shown at beginning of target life (BOL) and at end oftarget life (EOL).

FIG. 3 is a surface profile of a prior art sputtering target after about2000 kWhrs use.

FIG. 4A is a profile at BOL for a sputtering target having a modifiedprofile at the central region of the target according to an embodimentof the present disclosure.

FIG. 4B is a surface profile of the sputtering target of FIG. 4A afterabout 1500 kWhrs sputtering use.

FIG. 5 is a surface profile of a prior art sputtering target after 1500kWhrs use.

FIG. 6 is a surface profile of a sputtering target having a modifiedprofile at the central region after about 1500 kWhrs use.

FIG. 7 is a flow diagram illustrating a method for forming a targetincluding a modified central axis region according to an embodiment ofthe present disclosure.

FIG. 8 illustrates a sputtering target having a modified profileaccording to an embodiment of the present disclosure.

FIG. 9 illustrates the surface profile of the sputtering target of FIG.8 before and after 3950 kWhrs sputtering use according to an embodimentof the present disclosure.

FIG. 10A illustrates the surface profile of a reference target and amodified profile as shown in FIG. 8 and comparative surface profiles ofsame after 3000 kWhrs sputtering use.

FIG. 10B illustrates the surface profile of a reference target and amodified profile as shown in FIG. 8 and comparative surface profiles ofsame after 3500 kWhrs sputtering use.

FIG. 10C illustrates the surface profile of a reference target and amodified profile as shown in FIG. 8 and comparative surface profiles ofsame after 3950 kWhrs sputtering use.

FIG. 11A illustrates the surface profiles of sputtering targets havingmodified profiles according to an embodiment of the present disclosureand a prior art profile before sputtering use.

FIG. 11B illustrates the surface profiles of the sputtering targets ofFIG. 10A before and after 3950 kWhrs sputtering use.

FIG. 12A illustrates the surface profile of a reference target and amodified profile as shown in FIG. 11A and comparative surface profilesof same after 3000 kWhrs sputtering use.

FIG. 12B illustrates the surface profile of a reference target and amodified profile as shown in FIG. 11A and comparative surface profilesof same after 3500 kWhrs sputtering use.

FIG. 12C illustrates the surface profile of a reference target and amodified profile as shown in FIG. 11A and comparative surface profilesof same after 3950 kWhrs sputtering use.

FIG. 13 illustrates a sputtering target having a modified profileaccording to another embodiment of the present disclosure and areference profile.

FIG. 14 illustrates the surface profiles of the modified profile asshown in FIG. 13 after 1650 kWhrs and 1860 kWhrs sputtering use and areference profile after 1350 kWhrs sputtering use.

FIG. 15 is a flow diagram illustrating a method for designing a targetincluding a modified central axis region according to an embodiment ofthe present disclosure.

DETAILED DESCRIPTION

Physical vapor deposition (“PVD”) methodologies are used extensively forforming thin films of material over a variety of substrates. Variousmetals and alloys can be deposited using PVD technology, including forexample Al, Ti, Cu, Ta, Ni, Mo, Au, Ag, Pt and alloys of these elements.In one PVD process, known as sputter deposition or sputtering, particlesare ejected from the surface of a sputtering target by bombardment withgas ions, such as plasma. Thus, the sputtering target is the source forparticles, which are deposited onto a substrate, such as a semiconductorwafer. As the target is eroded during sputtering use, the surfacegeometry is altered. Changes in target surface geometry lead todifficulties depositing a uniform thin film by sputtering and such wearlimits target life.

Previously, problems related to depositing uniform thin films and/orextending target life have been addressed in various ways. Thoseinclude: i) increase of distance between target and wafer to allow onlycertain atoms with a specific ejection angle to reach the wafer; ii) useof a filtering device also called a collimator or flux optimizer; toselect only atoms with specific trajectories; iii) use of magnet withnew design, arrangement and movement; iv) application of a RF bias atthe wafer which enables a build of negative charge at wafer and forcemetal ions to deposit at angles close to wafer normal. All the abovesolutions have limitations. For example, increasing the distance betweenthe target source and the substrate or using a collimator is lessinefficient and leads to more waste of ejected atoms stuck in chamber oron the walls of collimator. Also application of a radio-frequency (RF)bias might result in electrical stress to the wafer components.

The most recent systems that use a collimator and/or new magnet designand movement also encounter problems. For the example of using acollimator as in the prior art, as shown schematically in FIG. 2, thereis a decrease in thin film uniformity through life (or equally anincrease in non-uniformity). Typically, from beginning of life (BOL) toend of life (EOL) of a sputtering target, deposition is characterized bya thinning at the center of the wafer compared to the edges. It is atleast in part due to the change in target erosion profile at the targetcenter 14 a at BOL to the target center 14 b at EOL. This affects thedirection at which atoms are ejected from the sputtering target throughlife relative to the location of collimator walls 24. For the example ofusing new magnet design and movement, there is a degradation of I-Vsputtering characteristics. Specifically voltage follows two trends withincreasing target life: i) an increase in voltage due to the change inspacing between the eroding target profile and magnet; in effect, thetarget surface becomes closer on average to the magnet located near thetarget backside; and, ii) an increase in voltage fluctuations caused asthe magnet moves between the in and out positions under the regions oftarget with deeper or shallower erosion grooves. As life increases, thetarget erosion profile becomes less uniform, which exacerbates the localdifferences in voltage.

Embodiments of the present disclosure address the problem of depositinguniformly thin films by addressing the target center profile andproposing new geometries for sputtering targets at the central area ofthe target. According to the present disclosure, the initial (i.e.before sputtering) target surface is strategically modified at thecenter of the target. The center of the target strategically modified isreferred to interchangeably herein as a central region, a central axisregion, a modified central axis region, and a modified profile includinga central axis region. Sputtering is sensitive to target shape andsurface profile. Electric field distribution in the vicinity of theplasma discharge depends on target shape and/or surface profile, becausethe target profile represents a boundary condition for the magnetic andelectric fields that are described by known laws of electromagnetism. Asa result, target shape will influence the local strength anddistribution of the electromagnetic field lines that in turn governdeposition rate and orientation of ejected atoms.

Moreover the mutual influence and interaction between a sputteringtarget and electromagnetic field evolves constantly during target lifebecause the profile of target surface changes as material is beingeroded away. This results in an ongoing re-distribution of the localstrength of electromagnetic field and causes a change in the directionof sputtered atoms.

It was discovered that over a sputtering target's lifetime, mechanismscontributing to the thinning of film deposited at the center of thewafer are impacted or affected at least in part to the center of thetarget having locally eroded very little during use and corresponding toa low sputtering rate in the center. As a consequence, a conventionalplanar (i.e., flat or non-profiled surface) 300 mm target having athickness of 25.4 mm (1 inch) and a radius of 221 mm (8.7 inches)retains almost the same height at the center, whereas the erosion in asurrounding region near the center, but typically at least about 25 toabout 50 mm (1 to 2 inches) away from the center, are typically high andresult in a deep eroded groove in the target at the end of life. Forexample, grooves of about 7.6 mm to about 12.7 mm (0.3-0.5 inches) indepth may be present at the end of life. An illustrative end of lifeerosion profile 26 of a 300 mm sputtering target having an initiallyflat or planar surface is shown in FIG. 3. As shown, the erosion profile26, also referred to as wear profile, of the target has a prominentprotuberance (also referred to as a hump or a bump) 30 at the centralregion 28 after about 2000 kWhrs use. The central region 28 has a radiusof about 50 mm (2 inches). A 300 mm target herein refers to the wafersize onto which the target sputters.

The protuberance 30 develops throughout a target's lifetime. The centralbump 30, having a height of about 10 mm (0.4 inches) or about 40% oforiginal target thickness disadvantageously blocks at least some atomsduring sputtering such as those having a trajectory represented by afirst set of arrows 32, because their trajectory crosses the centralprofile. This results in undesirable redeposition of atoms to thecentral area of the target. Most affected are those atoms dislodged fromthe surrounding area adjacent to protuberance 30, corresponding to thebottom 36 or side 38 of an erosion groove.

As central bump 30 is being formed by erosion, the slope 40 of thecentral bump 30 increases in steepness with further sputtering use asillustrated in the erosion profile 26 of FIG. 3. As a result, at leastsome atoms, represented by a second set of arrows 34, sputter in adirection away from axis 42 rather than in a direction toward the waferas would from the original planar target surface in the central region.Therefore atoms traveling in the direction of the second set of arrows34, which should have reached the wafer center area from the originaltarget surface, are now sputtered toward the side of the wafersubstrate. Trajectories 32 and 34 are undesirable in sputtering.

Moreover, the local geometrical relation and spacing between targetsurface and the collimator, referring again to FIG. 2 showing targetsurface 16 a at the beginning of target life and surface 16 b at the endof target life, changes the most in areas of profile having the biggestdifference between the local maximum and minimum in erosion. Thisdifference is the highest near the central bump and results in moreatoms having a change in sputtering direction between the beginning andend of life; as a result, a larger proportion of atoms are observed tobe captured in the central portion 25 of collimator 24 as shown in FIG.2. Therefore, at least those atoms captured by the collimator andadhering to the collimator walls do not reach wafer and contribute towafer thinning.

To solve the problem of wafer thinning, at least some embodiments of thepresent disclosure modify the profile of the central region of thetarget. Referring to FIGS. 4A and 4B, the target is modified at thecentral region in such a way that: a) the central bump of thecomparative erosion profile at end of life is smaller in height and b)the slope on both sides of the central bump at the end of life is not assteep as compared with a reference target. In at least some embodiments,this is accomplished by making a cavity 150, also referred tointerchangeably herein as a “concave curvature” or “concave feature”, inthe central portion of the target profile 100 of FIG. 4A. Profile 60 isa reference profile made of the same target material but having a planarprofile at the central region. Note that modified target profile 100 andreference target profile 60 are different in the central portion asshown but are overlapping or coincident in the remaining portion, thatis, at radial distance greater than about ±58.4 mm (about 2.3 inches).For a 25.4 mm (1 inch) thick target, the depth d₁ for the cavity canvary between about 1.3 mm and about 12.7 mm (about 0.050 inch and about0.5 inch). In other words, the cavity depth can be from about 5 percentto about 50 percent of the total target thickness, or from about 10percent to about 30 percent of the total target thickness, or from about15 percent to about 20 percent of the total target thickness. Forexample, in FIG. 4A, the cavity 150 has a maximum depth d₁ of 4.6 mm(about 0.18 inch). The radius in absolute value where the central partis modified depends on a specific initial target profile, target sourcematerial, and dimensions. Typically the modified central region includesa radius ranging from about 1.27 mm to up to about 89 mm (from about0.050 inch to up to about 3.50 inches) for a target with an overalltarget radius of 221 mm (8.7 inch). In FIG. 4A, the maximum radiusr_(max) where the central target profile is changed is about 58.4 mm(about 2.3 inch) for example. In other words, the cavity radius can befrom 5 percent to about 40 percent relative to the total target radius,or from 20 percent to about 30 percent relative to the total targetradius, or from about 23 percent to about 27 percent relative to thetotal target radius. The specific profile of the cavity can vary but ismostly determined by the central shape of erosion profile at the end oflife as is shown in FIG. 4B.

FIG. 4B illustrates the modified profile 110 corresponding to profile100 of FIG. 4A after about 1500 kWhrs sputtering use according toembodiments of the present disclosure. Profile 110 after 1500 kWhrscorresponds to a near end of life, which is about 2000 kWhrs for aconventional target. For comparison the profile 70 is shown in FIG. 4Bfor the reference target (having the initially planar central profile60) is illustrated. Notably, profile 110 is similar to reference profile70 after 1500 kWhrs except in the central region wherein theprotuberance 120 of profile 110 is significantly less pronounced thanthe protuberance 80 of reference profile 70, both in width and height.

The benefits of using modified profile 100 of FIG. 4A on the trajectoryof sputtered atoms after 1500 kWhrs use is shown schematically in FIG.6. The reference target profile after use is illustrated in FIG. 5 forcomparison. As shown in FIG. 5 for the prior art reference targetprofile 70 after 1500 kWhrs, the atoms include problematic trajectories,as represented by arrows 32 and 34, including redeposited atoms andatoms directed away from the central area of the wafer (headingdeferentially to the sides of the wafer) as similarly discussed for FIG.3. This is due to the prominent protuberance 80 blocking desiredtrajectories that would lead the atoms from the central region of thetarget to the central region of the wafer. In contradistinction, FIG. 6shows the modified profile 110 after 1500 kWhrs wherein the protuberance120, being smaller in both height and width, does not block desiredtrajectories, as represented by arrows 62 and 64, so that the sputteredatoms from the central region of the target are directed to the centralregion of the wafer. In other words, the modified profile 100 includingcavity 150 disposed in the central region (as shown in FIG. 4A) providestwo beneficial effects on the trajectory of central sputtered atoms aslife of the target progresses: (a) fewer atoms are hindered in theirtrajectory by the central bump 120 (of FIG. 4B and FIG. 6) because bump120 is not as high and wide as compared with the reference protuberance80 (of FIG. 4B and FIG. 5) resulting in a higher number of atoms likelyto reach the center of wafer; and, (b) the shape of central bump 120changes the overall distribution of sputtered atoms and the angulardirection of their trajectories, in other words sputtered atoms leavingthe bump area 120 are directed more toward the center of the wafer dueto the less steep slope on each side of the central bump resulting inmore vertically oriented ejection of central atoms and leading to ahigher proportion of central atoms passing through a flux collimator.Both of these effects reduce wafer thinning at the center and promotemore uniform deposition onto the wafer leading to improved wafer filmuniformity at the end of life.

Referring again to FIGS. 4A, 4B and 6, according to embodiments of thepresent disclosure, a sputtering target comprises a sputtering materialhaving a non-planar sputtering surface prior to erosion by use in asputtering system. The non-planar sputtering surface has a circularshape and comprises a central axis region 152 having a center axis 42.The central axis region 152 includes at least one non-protruding concavecurvature feature 150 symmetrically disposed about center axis 42 andhaving a first point, point 1, coincident with the center axis. The atleast one non-protruding concave curvature feature 150 corresponds to areference, protruding convex curvature feature 72 of an erosion profile70 of a reference sputtering target following erosion by use in asputtering system and coincident with center axis 42, the referencesputtering target comprising a sputtering material having an identicalcomposition as the sputtering material of the sputtering target, thereference sputtering target further comprising a planar sputteringsurface 60 prior to erosion by use in a sputtering system. Line 35 isperpendicular to center axis 42 and is colinear with the referencesputtering target planar sputtering surface 60 prior to erosion by usein a sputtering system. Point 1 is at a first axial distance 44 fromline 35. A surrounding region 155 is disposed about the central axisregion 152, in other words the surrounding region is further from centeraxis 42 and is non-overlapping with central axis region 152. Surroundingregion 155 includes a second point, point 2, coincident with line 35 andat a first radial distance 156 from center axis 42. The central axisregion 152 has a wear profile 110 after erosion by use in a sputteringsystem including a protuberance 115 having a third point, point 3,coincident with center axis 42 and at a second axial distance 46 fromline 35 and a fourth point, point 4, at the first radial distance 156from center axis 42 and at a third axial distance 48 from line 35,wherein third axial distance 48 is greater than or equal to first axialdistance 44 and to second axial distance 46.

Reference sputtering target having wear profile after use 70 includes afifth point, point 5, coincident with center axis 42 at a fourth axialdistance 50 from line 35, wherein first axial distance 44 and secondaxial distance 46 are greater than fourth axial distance 50.Protuberance 115 includes first outer circumferential wear surface 118having slope m₁ and the reference, protruding convex curvature feature72 after erosion includes a second outer circumferential wear surface 78having slope m₂, wherein m₁ is less steep than m₂. In at least someembodiments of the present disclosure, the non-protruding concavecurvature feature 150 includes an inner circumferential surface 145 anda bottom surface 148 including point 1. Bottom surface 148 can be flat.Alternatively, bottom surface 148 can be rounded, concave, or convex. Inother examples, bottom surface 148 can be pointed or angular (notshown).

The non-protruding concave curvature feature 150 of the sputteringtarget has a total target radius and a total target thickness. The shapeand dimensions of the non-protruding concave curvature feature can vary.In some embodiments, the first radial distance 156 is from about 5percent to about 40 percent relative to the total target radius and thefirst axial distance 44 is from about 5 percent to about 50 percent ofthe total target thickness. In other embodiments, the first radialdistance 156 is from about 20 percent to about 30 percent relative tothe total target radius and the first axial distance 44 is from about 10percent to about 30 percent of the total target thickness. In yet otherembodiments, the first radial distance 156 is from about 23 percent toabout 27 percent relative to the total target radius and the first axialdistance 44 is from about 15 percent to about 20 percent of the totaltarget thickness.

Sputtering targets according to embodiments of the present disclosuremay further comprise at least one recessed groove in the surroundingregion, for example grooves 82 and/or 84 as shown in FIG. 4A. Thesurrounding region can include the region between the central axisregion 152 reaching out to radial edge 86 of the target.

Referring again to FIGS. 4A, 4B and 6, according to embodiments of thepresent disclosure, a sputtering target comprising a sputtering materialand having a non-planar sputtering surface prior to erosion by use in asputtering system, the non-planar sputtering surface having a circularshape and comprising a central axis region 152 having a center axis 42.The central axis region 152 includes a concave curvature feature 150symmetrically disposed about the center axis 42 and having a firstpoint, point 1, coincident with the center axis 42. Concave curvaturefeature 150 corresponds to a reference, protruding convex curvaturefeature 72 of an erosion profile 70 of a reference sputtering targetfollowing erosion by use in a sputtering system for at least 1000 kWhrsand coincident with the center axis 42, the reference sputtering targetcomprising a sputtering material having an identical composition as thesputtering material of the sputtering target, the reference sputteringtarget further comprising a planar sputtering surface 60 prior toerosion by use in a sputtering system. Central axis region 152 has awear profile 110 after erosion by use in a sputtering system for atleast 1000 kWhrs including a protuberance 115. Protuberance 115 includesa first height, which is shown on FIG. 4B as the distance 48 less thedistance 46. Protuberance 115 further includes a first outercircumferential wear surface 118 having a first slope m₁. The reference,protruding convex curvature feature 72 includes a second height, whichis shown on FIG. 4B as the distance 48 less the distance 50. Reference,protruding convex curvature feature 72 further includes a second outercircumferential wear surface 78 having a second slope m₂. Protuberance115 provides a sputtered target having reduced shadowing relative to thereference, protruding convex curvature feature 72, as illustrated inFIGS. 5 and 6. The first height (distance 48 less distance 46 on FIG.4B) is less than the second height (distance 48 less distance 50 on FIG.4B), because the reference, protruding convex curvature feature 72having the second height blocks more sputtered atoms having trajectoriesdirected radially inward toward the central axis 42 and redepositingonto the target. Also shown, the first slope m₁ is less steep than thesecond slope m₂, so that the second outer circumferential wear surface78 directs more sputtered atoms with trajectories radially outwardrelative the central axis 42 away from a wafer. Sputtering materialincludes at least one material chosen from Ti, Al, Cu, Ta, Ni, Co, Mo,Au, Ag, Pt, W, Cr, a Ti alloy, an Al alloy, a Cu alloy, a Ta alloy, a Nialloy, a Co alloy, a Mo alloy, a Au alloy, a Ag alloy, a Pt alloy, a Walloy, and a Cr alloy. In some embodiments, the target is monolithic asis known in the art. In other embodiments, the target is diffusionbonded as is known in the art. The percentage reduction between theslope of the outer circumferential wear surface of the inventive targetof the present disclosure (e.g. first slope m₁ as in FIG. 4B) and theslope of the outer circumferential surface of the reference target (e.g.second slope m₂ as in FIG. 4B) in at least some of the embodiments ofthe present invention is at least about 40 percent. In otherembodiments, the percentage reduction between the slope of the outercircumferential wear surface of the inventive target of the presentdisclosure and the slope of the outer circumferential surface of thereference target is at least about 45 percent, or at least about 50percent, or at least about 55 percent, or at least about 60 percent, orat least about 65 percent, or at least about 70 percent, or at leastabout 75 percent, or at least about 80 percent, or at least about 85percent, or at least about 90 percent, or at least about 95 percent. Inat least some embodiments, the percentage reduction between the firstslope and the second slope is from about 40 percent to about 100percent. In these and other embodiments of the present disclosure, thecentral axis region 152 further includes a total target thickness at thecenter axis 42 in the central axis region 150 of the target prior tosputtering use, shown on FIG. 4A as distance t_(T) less distance 44,which is less than the total target thickness t_(T) of the referencetarget having a planar surface at the central axis region. In someembodiments, the total target thickness of the inventive target is fromabout 10 percent to about 30 percent less than the total targetthickness at the center axis for the reference sputtering targetcomprising the planar sputtering surface prior to erosion. In otherembodiments, the total target thickness is from about 15 percent toabout 25 percent less than the total target thickness at the center axisfor the reference sputtering target. In yet other embodiments, the totaltarget thickness is about 18 percent to about 22 percent less than thetotal target thickness at the center axis for the reference sputteringtarget. In some embodiments, the sputtering target further comprises atleast one recessed groove in the surrounding region 155.

At least some embodiments of the present disclosure include a method asillustrated in the flow diagram of FIG. 7 for forming a target includinga modified central axis region. The method can be tailored to a specifictarget configuration and source material as desired. A method ofmanufacturing a sputtering target comprising a sputtering materialhaving a non-planar sputtering surface prior to erosion by use in asputtering system, the non-planar surface having a circular shape,comprises the steps as shown if FIG. 7. In step 1000, the target isformed having a central axis region. The central axis region includes anon-protruding concave curvature feature symmetrically disposed about acenter axis and having a first point (point 1 of FIG. 4A) coincidentwith the center axis, wherein the at least one non-protruding concavecurvature feature corresponds to a reference, protruding convexcurvature feature of an erosion profile of a reference sputtering targetfollowing erosion by use in a sputtering system and coincident with thecenter axis. The reference sputtering target comprises a sputteringmaterial having an identical composition as the sputtering material ofthe sputtering target, and the reference sputtering target furthercomprises a planar sputtering surface prior to erosion by use in asputtering system. The first point at a first axial distance from a lineperpendicular to the center axis and colinear with the referencesputtering target planar sputtering surface prior to erosion by use in asputtering system. Step 1010 includes forming a surrounding regiondisposed about the central axis region; the surrounding region includinga second point (point 2 of FIG. 4A) coincident with the line and at afirst radial distance from the center axis. The method further includesoptimizing the first axial distance and the first radial distance. Instep 1020, the rate of erosion for a corresponding central axis regionand a corresponding surrounding region for the reference sputteringtarget is measured. In other words, the rate of erosion through life atvarious radii along the profile is measured and recorded experimentallyby sputtering a reference target through full life of the target. In atleast some embodiments, measurements are taken in about 2.54 mm (0.100inch) increments from edge to edge of the target surface. In step 1020,the erosion rate through life of any potential new candidate profile isassumed to be similar to that of prior art target. This assumptionremains acceptable to a first degree especially for the central area ofa target where sputtering is low for most target designs. The potentialnew candidate and reference target are made of the same material oralloy. Step 1030 includes calculating an erosion profile at end of lifefor the non-protruding concave curvature feature based upon said rate oferosion as determined in step 1020. Calculating as in step 1030 mayfurther include calculating a plurality of erosion profiles at end oflife for a plurality of non-protruding concave feature candidates togenerate a profile data set as in step 1040. The best candidate asselected from the plurality of non-protruding concave feature candidatesbased on the profile data set, as in step 1050, is used to form theoptimized target central axis region having a concave feature includinga point coincident with a center axis as in step 1060. According toembodiments of the method, the sputtering target can have a total targetradius and a total target thickness, wherein the first radial distanceis from about 5 percent to about 40 percent relative to the total targetradius and the first axial distance is from about 5 percent to about 50percent of the total target thickness. In other embodiments, the firstradial distance is from about 20 percent to about 30 percent relative tothe total target radius and the first axial distance is from about 10percent to about 30 percent of the total target thickness. In yet otherembodiments, the first radial distance is from about 23 percent to about27 percent relative to the total target radius and the first axialdistance is from about 15 percent to about 20 percent of the totaltarget thickness.

Materials suitable for sputtering targets according to embodiments ofthe present disclosure include pure elements and alloys. For example,suitable sputtering materials for a sputtering target include at leastone material chosen from Ti, Al, Cu, Ta, Ni, Co, Mo, Au, Ag, Pt, W, Cr,a Ti alloy, an Al alloy, a Cu alloy, a Ta alloy, a Ni alloy, a Co alloy,a Mo alloy, a Au alloy, a Ag alloy, a Pt alloy, a W alloy, and a Cralloy. In some embodiments, for targets made of a single element, suchas materials chosen from elemental Ti, Al, Cu, Ta, Ni, Co, Mo, Au, Ag,Pt, W, and Cr, the sputtering target is substantially pure or pure.Substantially pure means nearly pure or at least 99.9% by weightelemental content. For example, a suitable sputtering material for asputtering target can include at least one substantially pure materialchosen from Ti, Al, Cu, Ta, Ni, Co, Mo, Au, Ag, Pt, W, and Cr. In otherembodiments, the sputtering material of the sputtering target is analloy. An alloy includes a main element mixed with at least one otherelement from the periodic table, wherein the sputtering materialcontains a higher quantity of the main element than the one or moreelements with which it is mixed. According to standard namingconvention, an alloy may be referenced as an alloy of the main element.For example, an alloy in which the main element is Al is referenced asan Al alloy. Suitable sputtering materials for a sputtering target caninclude at least one main element chosen from Ti, Al, Cu, Ta, Ni, Co,Mo, Au, Ag, Pt, W, and Cr. Such materials may be referred to as a Tialloy, an Al alloy, a Cu alloy, a Ta alloy, a Ni alloy, a Co alloy, a Moalloy, a Au alloy, a Ag alloy, a Pt alloy, a W alloy, and a Cr alloy,respectively.

In step 1020, a plurality of varying profiles at the central region isdesigned representing candidate designs. Step 1020 further includespredicting the profile at the central region for the candidate designsat a plurality of life stages (progressively relating to time of use inkWhrs) for the plurality of varying profiles using referencecalculations for the a corresponding plurality of life stages for thereference target as determined by the experimental measurements oferosion rate as a function of time of use as determined in step 1000. Instep 1030, the predicted profiles over life for candidate designs areevaluated and the best candidate design is selected based on thedimensions and shape of the central part of profile toward the end oflife. In addition, step 1040 optionally includes modeling of theinteractions between the local electromagnetic field and the targetsurface to ascertain the angle distribution of sputtered atoms at thetarget center.

Advantageously, and according to at least some embodiments of thepresent disclosure, modified profiles having a central region cavity areuseful with either monolithic target designs or diffusion bonded targetdesigns.

In some embodiments, the sputtering targets including a non-protrudingconcave curvature feature according to the present disclosure aremonolithic. In other words, sputtering targets having a central regioncavity may be formed from one single piece. These targets are referredto interchangeably herein as monolithic and/or monoblock assemblies.Monolithic designs, being composed of a single material, can providebetter control of electro-magnetic properties including voltagevariations within a sputtering target.

In other embodiments according to the present disclosure, sputteringtargets are coupled or attached to a backing plate by, for example,diffusion bonding. At least some embodiments of the present disclosureinclude wherein the target is diffusion bonded. The sputtering targetmay further comprise a backing plate. Use of a backing plate as with thediffusion bonded targets can provide support for the sputtering targetduring the sputtering process to advantageously reduce, for example,warping of the sputtering target over the life of the target. Onenon-limiting example of a method of attaching a sputtering target to abacking plate is hot isotactic pressing (“HIPing,” or “hipping”).Hipping may be used to diffusion bond the sputtering target to a backingplate by pressing the sputtering target and backing plate together afterheating to a hipping temperature. Targets made of Ti are examples ofdiffusion bonded targets having a central region cavity. In the case ofdiffusion bonded designs, the backing plate material is different thanthe core target material and thus may have different electro-magneticand other physical properties such as CTE, electrical resistivity, andthermal conductivity. These differences between the core and backingplate materials can exacerbate local voltage differences. Therefore,backing plate selection must be carefully taken into accountelectro-magnetic and physical properties to complement those of thetarget core material. Typically, controlling and predicting localfluctuations during erosion in diffusion bonded designs is morechallenging as compared to monolithic designs. The sputtering target mayfurther comprise a backing plate comprising a grooved flange, whereinthe grooved flange may further be recessed to provide, for example,cooling.

For both monolithic designs and for backing plate designs, the targetmaterial may be processed, for example with a thermo-mechanical (TMP)process, to enhance the strength of the target. For example, Al, Alalloys, Cu and Cu alloys, which have a low strength when grain size islarge (typically 30-100 microns), may be processed with TMP process toincrease the strength of the material.

One particularly effective TMP process is Equal Channel AngularExtrusion (ECAE), techniques of which are disclosed in U.S. Pat. No.5,850,755, U.S. Pat. No. 7,191,630, and U.S. Pat. No. 7,767,043, whichare incorporated herein by reference in their entirety. According to atleast some embodiments of the present disclosure, ECAE can be usedadvantageously to impart severe plastic deformation in bulk pieces ofmetals and alloys and give additional strength to those materials. ECAEis an extrusion technique, which consists of two channels of roughlyequal cross-section meeting at a certain angle, where the angle rangesbetween from about 90° to about 140°. In one embodiment, the angle is90°. Under conditions providing good lubrication of billet and walls,uniform simple shear deformation occurs layer by layer at theintersecting plane between the two channels. The main processcharacteristics of ECAE are (i) high deformation per pass (at 90°, truestrain is 1.17); (ii) multi-pass ECAE can reach extreme levels ofdeformation without changing the shape and volume of the billet aftereach pass; (ii) rotation or flipping of the billet between each pass canachieve various strain paths to control grain shape and crystallographictexture. Two main mechanisms for strengthening during ECAE are hereindescribed. Firstly, refinement of structural units, for example cells,sub-grains and grains, to submicron levels. This is also referred to asHall Petch strengthening:

$\sigma_{y} = {\sigma_{0} + \frac{k_{y}}{\sqrt{d}}}$where σ_(y) is the yield stress, σ_(o) is a materials constant for thestarting stress for dislocation movement (or the resistance of thelattice to dislocation motion), k_(y) is the strengthening coefficient(a constant specific to each material), and d is the average graindiameter. Based on this equation, strengthening becomes particularlyeffective when grain diameter d is less than 1 micron. The second mainmechanism for strengthening during ECAE is the presence of a pluralityof dislocations within the cells, sub-grains, and grains due to highstrain.

Other effective TMP processes to impart strength in materials includehardening steps by conventional methods such as rolling, drawing,extrusion or forging that are performed in materials after arecrystallization heat treat step. In some embodiments of the presentdisclosure, hardening yields targets having a central region cavityhaving an average grain size in the range from about 30 microns to about100 microns; such targets include Al alloys and Cu alloys andpractically achievable strength is in the intermediate range between alow strength fully recrystallized material and a high strength submicronECAE material. For some Al and especially Cu alloys as well as hardermaterials such as Ti, Ta, Co, Cr, W, Ni such as a solution can offersufficient strength for a monolithic design.

In general, a high strength material, such as for example obtained viaECAE, is especially advantageous in monolithic design because a strongermaterial can be sputtered deeper and therefore longer. For example,depending on design, life of 200 mm/300 mm monolithic targets can betypically extended by 20%-100% compared to standard diffusion bondedtargets when using ECAE materials.

High strength ECAE materials with submicron grain structures and, to alesser extent, of conventionally hardened materials can provide areduction of voltage fluctuations. These reductions in voltagefluctuations can include a reduction of Eddy currents due to a slightlyhigher electrical resistivity. This contributes positively in thereduction of voltage fluctuations, plasma instabilities and DC powerfaults. Further, reductions in voltage fluctuation can include a betterresistance against target warping through life, a phenomenon thatincreases with life. Less warping allows a better consistency of thedistance between the magnet and the erosion profile thru life, which inturn is directly related to local voltages. Therefore, a better controlof voltage fluctuations can be obtained. Furthermore one should alsonote that the usage of a central region cavity in the target profileaccording to at least some of the embodiments of the present disclosureweakens the overall mechanical strength of a target assembly. Promotinga higher strength in target material becomes therefore even moreimportant and beneficial in order to limit target deflection.

In at least some of the embodiments of the present disclosure, variousgeometries of the backside of target assembly are suitable. For example,the backside of the target assembly may include channels, which improvecooling efficiency and contributes in a reduction of target deflection.Another advantage of features such as channels at the target backside isa reduction of Eddy currents, which also helps decrease plasmainstabilities.

At least some embodiments of the present disclosure are illustrated bythe following non-limiting examples.

Example 1

FIG. 8 is the beginning of life surface profile for a reference target(profile 90) and a target having a modified profile (profile 130), whichincludes a central cavity region according at least some embodiments ofthe present disclosure. The reference target and the target having themodified profile were both 300 mm Cu alloy monolithic targets having thesame composition and were subjected to the same ECAE processingconditions. The targets differed in the surface profiles. The centralportion of profile 130 has a 4.57 mm (0.18 inch) deep cavity withinradii+/−58.4 mm (2.3 inch). The total target thickness for the targethaving profile 130 is 17.8 mm (0.7 inch), which is an 18.9% reduction inthickness as compared with the target having reference profile 90. Thetarget having profile 130 used a monolithic design configuration with ahigh strength submicron ECAE Cu alloy to allow for providing mechanicalstability. The standard reference profile 90, without modification atthe central region is also shown for comparison.

The profile 130 target reached 3,950 kWhrs, which represents anadditional 450-650 kWhrs in life as compared to a ECAE Cu alloymonolithic target having the profile 90 that runs typically up to3300-3500 kWhrs. One reason for this substantial life extension isimproved film uniformity. Without being bound by theory, it is believedthat profile 130 modified in the central region allowed more atoms toreach the central portion of wafer wherein the trajectories of thesputtered atoms were not hindered by the excessive protuberance of thestandard target.

The life improvement for target having profile 130 as compared the lifefor a standard diffusion bonded target for same chamber configuration isaround 2200-2400 kWhrs, thereby showing target life extended by about65% to about 80%.

The erosion profiles before and after sputtering are illustrated in FIG.9 as profile 130 and profile 140 respectively. Profile 140 was recordedafter 3950 kWhrs sputtering use. The deepest erosion area sputtered 89%of the target thickness, i.e. only about 2.79-3.05 mm (0.11-0.12 inch)was left at the deepest groove. This represents close to the maximumachievable limit for target life for this design. Even for this nearoptimal case with extended life, the overall target warping was low witha maximum of 0.69 mm (0.027 inch) toward magnet and no evidence ofcontact between the target and the magnet was found.

FIGS. 10A-10C illustrates the evolution of profiles for the referenceand modified targets at various times in life for the targets as shownin FIG. 8 having reference profile 90 and modified profile 130 atbeginning of life (BOL). FIG. 10A illustrates reference profile 90target at BOL (0 kWhrs) and corresponding profile 90A after 3000 kWhrs;and modified profile 130 target at BOL (0 kWhrs) and correspondingprofile 130A after 3000 kWhrs of sputtering. FIG. 10B illustratesreference profile 90 target at BOL (0 kWhrs) and corresponding profile90B after 3500 kWhrs; and modified profile 130 target at BOL (0 kWhrs)and corresponding profile 130B after 3500 kWhrs of sputtering. FIG. 10Cillustrates reference profile 90 target at BOL (0 kWhrs) andcorresponding profile 90C after 3950 kWhrs; and modified profile 130target at BOL (0 kWhrs) and corresponding profile 140 after 3950 kWhrsof sputtering. As the targets having BOL profile 90 (reference) andprofile 130 (modified according to Example 1) erode, there aredifferences in height and slope for the central cavity region. Asillustrated in FIG. 10C, the slope M2 of profile 90C is steeper than theslope M1 of profile 140, each slope taken after 3950 kWhrs ofsputtering. Table 1 includes data for the slopes, M1 and M2, calculatedat various times of life including at 2500, 3000, 3500, and 3950 kWhrs.The slope of the profile 130 target was significantly reduced from about−43% to about −50% as compared with the slope of the profile 90reference target at sputtering times ranging from 2500 to 3950 kWhrs.

TABLE 1 Slopes for Reference Profile 90 Target and Modified Profile 130Target at Various Times of Sputtering Life Slope of Slope of % reductionin profile 90 profile 130 slope between Life target target M1 and M2Ratio (kWhrs) (M2) (M1) [(M1 − M2)/M2] (M1/M2) 2500 0.294 0.153 −48%0.52 3000 0.355 0.176 −50% 0.50 3500 0.417 0.225 −46% 0.54 3950 0.4720.270 −43% 0.57

Example 2

A 300 mm Cu alloy target having a modified profile including a centralcavity region according at least some embodiments of the presentdisclosure is provided as profile 160 as shown in FIG. 11A beforesputtering and as profile 170 after 3950 kWhrs in FIG. 11B. Compared tothe profile 130 described in Example 1, the profile 160 includes atleast one modification in the central region in that profile 160includes a deeper central cavity of about 7.6 mm (about 0.3 inch).Profile 160 also includes a change in profile between radii 88.9 and139.7 mm (3.5 and 5.5 inch) and by symmetry between −88.9 and −139.7 mm(−3.5 and −5.5 inch).

FIGS. 12A-12C illustrates the evolution of profiles at various times insputtering life for the targets having reference profile 90 and modifiedprofile 160 at beginning of life (BOL). FIG. 12A illustrates referenceprofile 90 target at BOL (0 kWhrs) and corresponding profile 90A after3000 kWhrs; and modified profile 160 target at BOL (0 kWhrs) andcorresponding profile 160A after 3000 kWhrs of sputtering. FIG. 12Billustrates reference profile 90 target at BOL (0 kWhrs) andcorresponding profile 90B after 3500 kWhrs; and modified profile 160target at BOL (0 kWhrs) and corresponding profile 160B after 3500 kWhrsof sputtering. FIG. 12C illustrates reference profile 90 target at BOL(0 kWhrs) and corresponding profile 90C after 3950 kWhrs; and modifiedprofile 160 target at BOL (0 kWhrs) and corresponding profile 170 after3950 kWhrs of sputtering. As the targets having BOL profile 90(reference) and profile 160 (modified according to Example 2) erode,there are differences in height and slope for the central cavity region.Table 2 includes data for the slopes, M2 and M3, calculated at varioustimes of life including at 3000, 3500, and 3950 kWhrs. The slope of theprofile 160 target was dramatically reduced from about −77% to about−96% as compared with the slope of the profile 90 reference target atsputtering times ranging from 3000 to 3950 kWhrs.

TABLE 2 Slopes for Reference Profile 90 Target and Modified Profile 160Target at Various Times of Sputtering Life Slope of Slope of % reductionin profile 90 profile 160 slope between Life target target M3 and M2Ratio (kWhrs) (M2) (M3) [(M3 − M2)/M2] (M3/M2) 3000 0.355 0.015 −96%0.04 3500 0.417 0.064 −85% 0.15 3950 0.472 0.108 −77% 0.23

Profile 160 provides an even thicker film at target center at the end oflife, which is believed to result in a better wafer film uniformity atthe end of life, than profile 130. This is due to the reduction inheight of the central bump as well as the absence of steep slope on eachside of central bump for profile 170 as compared with profile 140.

Also the new profile 160 provides a better resistance against voltagefluctuations and ultimately DC power faults. As shown in FIG. 10B, thenew profile reduces the height of the locally less eroded area at radiusbetween 88.9 and 139.7 mm (3.5″ and 5.5″) in absolute value at the endof life. This in effect decreases the difference in height between thatlocation and the adjacent areas that have more erosion and results inless voltage variations.

Example 3

FIG. 13 is the beginning of life surface profile for a reference target(profile 190) and a target having a modified profile (profile 230),which includes a central cavity region according at least someembodiments of the present disclosure. As shown in FIG. 13, the centralportion of profile 230 has a 3.30 mm (0.13 inch) deep cavity withinradii+/−40.6 mm (1.6 inch). Profile 230 also includes a maximumthickness 26.7 mm (1.05 inch) in the surrounding region, which isgreater than the maximum thickness of profile 190 of 25.4 mm (1.0 inch).Profile 230 further includes a reduced thickness at the circumferentialouter edge of the target.

FIG. 14 illustrates the evolution of profiles at various times insputtering life for the targets. Profile 195 after 1350 kWhrs, which isthe end of life, corresponds to the target having reference profile 190at beginning of life (BOL). Profiles 240 and 250 show the profiles after1650 kWhrs and 1850 kWhrs, respectively, for the modified target havingprofile 230 target at BOL (0 kWhrs). Profile 195 at 1350 kWhrs andprofile 250 at 1850 kWhrs show the end of life for the reference andmodified targets having initial profiles 190 and 230 respectively. Theimprovement in life for the modified target having initial profile 230,as compared with profile 190, is due to better wafer uniformity.

At least some embodiments of the present disclosure include a method asillustrated in the flow diagram of FIG. 15 for designing a targetincluding a modified central axis region. The method can be tailored toa specific target configuration and source material as desired. A methodof designing a sputtering target comprising a sputtering material havinga non-planar sputtering surface prior to erosion by use in a sputteringsystem, the non-planar surface having a circular shape, comprises thesteps as shown in FIG. 15. Step 2000 includes forming a sputteringtarget having a profiled surface having a concave curvature featuresymmetrically about a central axis of the sputtering target. Step 2010includes measuring a sputtered profile of the sputtering target aftersputtering in a sputtering chamber. Step 2020 includes designing arevised surface profile based on the measurements of the sputteredprofile to reduce shadowing at a central axis region of the sputteringtarget. Step 2030 includes forming a revised sputtering target havingthe revised surface profile. If needed, steps 2010 through 2030 may berepeated to optimize the surface profile.

In the foregoing, all temperatures are set forth uncorrected in degreesCelsius and, all parts and percentages are by weight, unless otherwiseindicated.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

The invention claimed is:
 1. A sputtering target comprising a sputteringmaterial having a non-planar sputtering surface prior to erosion by usein a sputtering system, the non-planar sputtering surface having acircular shape and comprising: a central axis region having a centeraxis; the central axis region including at least one non-protrudingconcave curvature feature symmetrically disposed about the center axis,wherein a bottom surface of the at least one non-protruding concavecurvature feature has a convex shape and the convex shape having a firstpoint on the center axis; and a surrounding region disposed about thecentral axis region, the surrounding region comprising a top planarsurface and at least one recessed groove, wherein the first point isbelow the top planar surface of the surrounding region, and abottom-most surface of the bottom surface of the at least onenon-protruding concave curvature feature is below a bottom surface ofthe at least one recessed groove; wherein a distance from the top planarsurface of the surrounding region to the first point is about 15 percentto about 30 percent of a total thickness of the sputtering target, andthe at least one non-protruding concave curvature feature extendsradially from the center axis a radial distance of from about 5 percentto about 40 percent relative to a total radius of the sputtering target.2. The sputtering target of claim 1, wherein the sputtering materialincludes at least one material chosen from Ti, Al, Cu, Ta, Ni, Co, Mo,Au, Ag, Pt, W, Cr, a Ti alloy, an Al alloy, a Cu alloy, a Ta alloy, a Nialloy, a Co alloy, a Mo alloy, a Au alloy, a Ag alloy, a Pt alloy, a Walloy, and a Cr alloy.
 3. The sputtering target of claim 1, wherein theleast one non-protruding concave curvature feature extends radially fromthe center axis the radial distance of from about 20 percent to about 30percent relative to the total radius of the sputtering target.
 4. Thesputtering target of claim 1, wherein the at least one non-protrudingconcave curvature feature extends radially from the center axis theradial distance of from about 23 percent to about 27 percent relative tothe total radius of the sputtering target.
 5. The sputtering target ofclaim 1, wherein the distance from the top planar surface of thesurrounding region to at the first point is about 15 percent to about 20percent of the total thickness of the sputtering target.
 6. A sputteringassembly comprising: a backing plate; and the sputtering targetaccording to claim 1 bonded to the backing plate.
 7. The sputteringassembly of claim 6, wherein the sputtering target is diffusion bondedto the backing plate.